The present invention relates to a novel ceramic electrostatic chuck with built-in heater or, more particularly, relates to a ceramic-made electrostatic chuck with built-in heater used in the processing of electronic devices for heating and cooling of a work piece under firm holding by the electrostatic attractive force of the electrostatic chuck.
In the manufacturing process of various semiconductor devices, the work piece such as a semiconductor silicon wafer is sometimes heated to an elevated temperature under firm holding on a ceramic-made heater plate. A most conventional means for holding a silicon wafer under processing is a so-called electrostatic chuck which can be used even in vacuum where traditional vacuum-sucking chucks can no longer work for sucking. When a silicon wafer as a work piece to be processed is desired to be heated under firm holding, it is a due idea to use an electrostatic chuck provided with a built-in heater (see, for example, Japanese Patent Kokai 4-358074). The ceramic electrostatic chuck with built-in heater disclosed there typically has a structure consisting of a base plate of a ceramic material such as a sintered body of boron nitride, an electrode layer formed on a surface of the base plate from pyrolytic graphite, a heater element layer formed on the other surface of the base plate also from pyrolytic graphite and an insulating ceramic layer formed on the electrode layer and the heater element layer from, for example, pyrolytic boron nitride. It is a trend accordingly that the dielectric material of the electrostatic chuck is under continuous replacement of conventional synthetic resins with a ceramic material as is disclosed in Japanese Patent Kokai 52-67353 and 59-124140.
The above mentioned ceramic electrostatic chuck with built-in heater has a problem in respect of the durability of the material of the base plate which is a sintered body of boron nitride because sintered bodies of boron nitride have a thermal expansion coefficient which is quite different from the coefficient in the pyrolytic graphite forming the electroconductive layer and the pyrolytic boron nitride forming the insulating layers, i.e. the electrode layer and the heater element layer, so that troubles are sometimes unavoidable when the ceramic electrostatic chuck is subjected to repeated cycles of heating and cooling to cause exfoliation of layers and crack formation in the ceramic body under thermal stress.